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SubjectRe: Why side-effects on open(2) are evil. (was Re: [RFD w/info-PATCH]device arguments from lookup)
Malcolm Beattie writes:
> Andreas Dilger writes:
> > PS - I used to think shrinking a filesystem online was useful, but there
> > are a huge amount of problems with this and very few real-life
> > benefits, as long as you can at least do offline shrinking. With
> > proper LVM usage, the need to shrink a filesystem never really
> > happens in practise, unlike the partition case where you always
> > have to guess in advance how big a filesystem needs to be, and then
> > add 10% for a safety margin. With LVM you just create the minimal
> > sized device you need now, and freely grow it in the future.
> In an attempt to nudge you back towards your previous opinion: consider
> a system-wide spool or tmp filesystem. It would be nice to be able to
> add in a few extra volumes for a busy period but then shrink it down
> again when usage returns to normal. In the absence of the ability to
> shrink a live filesystem, storage management becomes a much harder job.
> You can't throw in a spare volume or two where it's needed without
> careful thought because you'll be ratchetting up the space on that one
> filesystem without being able to change your mind and reduce it again
> later. You'll end up with stingy storage admins who refuse to give you
> a bunch of extra filesystem space for a while because they can't get it
> back again afterwards.

I suppose it depends a bit on how your system is administered. On LVM
systems, I tend to allocate new volumes for special situations like this.
When the special need is gone, you simply remove the whole thing. Yes,
this is a bit of a hack for not having online shrinking, but I have not
really had a _big_ need to do that.

The only time I've really needed online shrinking is when someone
screwed up and made / or /var way too huge for some (bad) reason and
you can't unmount it conveniently. Under AIX, you can't shrink JFS
even unmounted so it meant backup/restore. Even so, having empty
space in a filesystem is not a reason to panic, while having no free
space in a filesystem _is_ a reason to panic, hence online growing
of ext2.

Cheers, Andreas
Andreas Dilger \ "If a man ate a pound of pasta and a pound of antipasto,
\ would they cancel out, leaving him still hungry?" -- Dogbert
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